Plasticity and structure evolution of ferrite and martensite in DP 1180 during tension and cyclic bending under tension to large strains

This paper describes the main results obtained from a detailed experimental investigation into dislocation and twinned structures that develop in dual phase (DP) steel sheets. In particular, morphology defect-structures present DP 1180 having 55% ferrite 45% martensite, were examined using transmission electron microscopy (TEM). Microstructure of as-received consists twin-free martensite form lath island morphologies exhibiting relatively low content (3.41 × 108 cm?2). The was deformed simple tension (ST) to fracture continuous-bending-under-tension (CBT) six cycles. As CBT test facilitates stretching sheet considerably beyond point necking, strength increases substantially exceeds achieved ST at fracture. consequence plastic deformation, nano-twins are found island-shaped while lath-shaped remains twin-free. Additionally, some regions needle-like after CBT. density matrix with strain, accumulations dislocations near ferrite/martensite interface ferrite. Unlike ST-deformed samples, high (1.47 109 cm?2) tangles observed processed sample. We propose primary mechanisms enabling achievement strength, maintaining residual ductility upon intense slip profuse nano-twinning regions.